[labnetwork] Conductivity Standard Solution

Thu Feb 5 14:21:39 EST 2015

Dear John,

We do have a resistivity meter mounted on the system, just before [few
meters] from tap. And that reads ~18 Mohm. And whenever it drops that is
the time we change the filters/beds and do maintenance.

I think we need to monitor that meter regularly and need not to check at
the tap, though its few meters away.

Thanks,
Kamal.

On Mon, Feb 2, 2015 at 11:29 PM, John Shott <shott at stanford.edu> wrote:

>  Kamal:
>
> OK, I understand that you do not have a circulating system.  I suspect
> that this is a "once through" system where water goes through a certain
> number of polishing beds, UV, and final filters before heading directly to
> your DI taps.  I've run systems of that type.
>
> I personally don't think that calibration of your resistivity monitors is
> the thing that you should worry about. Even if your conductivity measures
> 0.04 uS/cm ... which, yes, is technically impossible because at room
> temperature water can be no less than 0.055 uS/cm ... that is indicative of
> high-resistivity water.  If the conductivity increased to 0.08 uS/cm,
> however, then you know that something has changed.
>
> I would suggest that you try to get the appropriate adapter in your supply
> line so that you can install a permanent mounting point for your
> resistivity monitor.  In that way, you can look at your conductivity any
> time that you are flowing water.  You can also answer the question in a
> once through system: how long after I begin flowing water, does the
> conductivity fall to the point that I am getting good resistivity water.
> Most importantly, if you normally see a conductivity of 0.04 uS/cm, and it
> increases to 0.08 uS/cm, for example, you know that something has changed.
> That might be indicative, for example, that it is time to change your resin
> beds.
>
> While absolute calibration is nice, with all due respect to my friends at
> NIST, not all instruments need to be fully calibrated to provide useful
> diagnostic information.  I believe that this may be one of those cases
> where being able to detect a change in conductivity may be more important
> than the absolute accuracy of the conductivity measurement.
>
> Good luck,
>
> John
>
>
> On 2/2/2015 4:22 AM, Kamal Yadav wrote:
>
> Dear John, Noah, and Miller,
>
>  Thank you for your response. I have gone through the attachment sent by
> John and Noah, which is identical and discusses about the topic in detail.
> I did not know this one is going to be difficult as well...
>
>  We do not have a circulating DI water loop. We have a conductivity meter
> using which we try to periodically check the DI water resistivity in
> flowing condition in a beaker waiting for sufficient time. I was happy as
> it was showing 0.04 uS/cm :) as that would be around 25 Mohm-cm much more
> than 18.2 Mohm, until a faculty pointed out that it is theoretically
> impossible at that temperature and is evident from the attachments you sent.
>
>  We have another resistivity meter in Solar Cell Center, that one is new
> and gives good reading something on which we can believe, so far.
> Calibrating that meter after sometime need to be identified as informed  by
> the supplier [Merc Millipore]. They do not know as of now!!
>
>  *Two Options I can see: [John, Noah, Miller, please comment].*
>
>  1. These days 1 uS/cm standard is also available at NIST. But still far
> from ~ 0.055.  The attachment claims ASTM standard even at 100 uS/cm can be
> used to calibrate UPW range resistivity meter? I am little confused whether
> I can use the standard, and whether it will be stable with its
> conductivity. We are ok as long as it shows more than 16 or 17 MOhm,..but
> certainly not 25 :). The good meter from Solar cell lab shows around 15
> Mohm-cm so we know it may be accurate. Since it is flowing DI water in a
> beaker it would be little far from 18.2 compare to John's 17.5, I suppose!
>
>  2. Send out the meter to an outside agency, will work if agency is in
> India, otherwise I need to see how much it cost, which may be equal to buy
> a new one.
>
>
>  Thanks,
> Kamal.
>
>
>
>
>
>
>
>
>
>
>
> On Sat, Jan 31, 2015 at 12:03 AM, Noah Clay <nclay at seas.upenn.edu> wrote:
>
>> Kamal,
>>
>>  Personally, I would send out your meter(s) for calibration by an
>> expert.  That said, here’s a reference from a company in the Boston area
>> (google search: "calibrate ultrapure water conductivity meter”)
>>
>>  http://www.snowpure.com/docs/thornton-upw-resistivity-measurement.pdf
>>
>>  Apparently, one can purchase standards from NIST for this (as stated in
>> the above link), but I’m not sure if they have a standard in your range.
>>
>>  Here’s another link from the same search/query:
>>
>>
>> http://www.thermoscientific.com/content/dam/tfs/ATG/EPD/EPD%20Documents/Application%20&%20Technical%20Notes/Water%20Analysis%20Instruments%20and%20Supplies/Lab%20Electrodes%20and%20Sensors/Ion%20Selective%20Electrodes/AN-PUREWATER-E%20RevA-HIGHRES.pdf
>>
>>  Best of luck,
>> Noah Clay
>>
>>  *Director, Quattrone Nanofabrication Facility*
>> *School of Engineering & Applied Sciences*
>> *University of Pennsylvania*
>> *nano.upenn.edu <http://nano.upenn.edu>*
>>
>>
>>   On Jan 30, 2015, at 11:12 AM, John Shott <shott at stanford.edu> wrote:
>>
>>    Kamal:
>>
>> Let me start by saying that I've never actually tried to calibrate meters
>> of this type.  Why?  Because it is not easy.  Here is a good reference
>> article from over 15 years ago that describes the process in great detail
>> including the fact that the standard conductivity solutions only go down to
>> about 5 uS/cm ... which isn't very close to the 0.06 uS/cm you are hoping
>> to measure.  They also talk about separating the whole calibration process
>> into the steps of calibrating the meter itself (easy), the temperature
>> probe (reasonably easy), and the "cell constant" of the probe itself
>> (hard).  A number of you will recognize that the author of this paper works
>> for a company that makes and sells resistivity probes and monitors.  This
>> is not intended to be an endorsement of that, or any other, company ...
>> but, I think, indicates that detailed calibration of DI resistivity
>> monitoring systems is typically found primarily in the companies that make
>> and sell such instrumentation rather than by the folks that use such
>> instrumentation.
>>
>> Their solution for high-precision calibration was to measure UHP water
>> over a range of temperatures as a means of determining and/or calibrating
>> the cell constant.  If you read this article, however, you will conclude
>> that this is not a procedure for the faint of heart.
>>
>> In recirculating DI systems, I believe that it is more common to have
>> continuous resistivity monitoring on both the supply side and return side
>> of the system.  In our case, we typically see supply and return resistivity
>> readings about 17.7 MOhm-cm or higher ... but that rarely, if ever, read
>> the theoretically expected 18.2 MOhm-cm.  In fact, it is not uncommon to
>> see a return resistivity that is slightly higher than the supply-side
>> resistivity ... which would seem unlikely.
>>
>> Then, on an occasional basis ... probably not as frequently as we should
>> ... we (well, a third-party analytical laboratory) collect samples and have
>> them measured for particle content, bacteria grown, total oxidizable
>> carbon, dissolved silica, and a 30-element mass-spec analysis for metal
>> levels in the ppt range that is commonly used for DI systems.  In short,
>> there are lots of things that CAN be wrong with DI water that are not seen
>> by even an accurate resistivity measurement.  In other words, as long as
>> our resistivity readings are on the order of 17.5 MOhm-cm or above on both
>> supply and return lines, I, for one, don't worry about the resistivity
>> aspects of our water.  In fact, earlier this week, I was comparing these DI
>> analytical test results with another frequent contributor to this forum
>> from the Bay Area institution with the longest history as a university
>> laboratory in this field.
>>
>> Finally, when you say "periodic monitoring" do you mean that you have a
>> probe in a continuously recirculating loop and you want to look at the
>> resistivity of that periodically ... or that you occasionally collect a
>> sample of water and are trying to measure it's resistivity?  If it is the
>> latter, that can be tricky: when exposed to air, DI water absorbs CO2 which
>> forms carbonic acid that can cause your resistivity numbers to degrade.
>>
>> My guess is some of the folks that run newer labs than ours will have
>> more details about the way that they monitor the DI water in these newer
>> operations.
>>
>> Let me know if you have any additional questions.
>>
>> John
>>
>> On 1/30/2015 2:01 AM, Kamal Yadav wrote:
>>
>> Dear All,
>>
>>  What is the best way to calibrate conductivity meters for DI water
>> resistivity periodic monitoring.
>>
>>  Standard known conductivity solutions are available but which one is
>> good and stable for this range of measurement. [18 MOhm-cm or ~ 0.06 uS/cm]
>>
>>  Thanks a lot!
>>
>>  --
>>  Thanks,
>>  Kamal Yadav
>> Sr. Process Technologist
>>  IITBNF, EE Department, Annexe,
>> IIT Bombay, Powai
>> Mumbai 400076
>> Internal: 4435
>> Cell: 7506144798
>> Email: kamal.yadav at gmail.com, kamalyadav at ee.iitb.ac.in
>>
>>
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>>
>>   <thornton-upw-resistivity-measurement.pdf>
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>>
>>
>
>
>  --
>  Thanks,
>  Kamal Yadav
> Sr. Process Technologist
>  IITBNF, EE Department, Annexe,
> IIT Bombay, Powai
> Mumbai 400076
> Internal: 4435
> Cell: 7506144798
> Email: kamal.yadav at gmail.com, kamalyadav at ee.iitb.ac.in
>
>
>

-- 
Thanks,
Kamal Yadav
Sr. Process Technologist
IITBNF, EE Department, Annexe,
IIT Bombay, Powai
Mumbai 400076
Internal: 4435
Cell: 7506144798
Email: kamal.yadav at gmail.com, kamalyadav at ee.iitb.ac.in
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